Wear-resistant alloys having complex microstructure

ABSTRACT

A wear-resistant alloy having a complex microstructure is provided. The microstructure includes a range of about 28 to about 38 wt % of zinc (Zn),a range of about 1 to about 3 wt % of tin (Sn), a range of about 6.2 to about 9.4 wt % of silicon (Si), and a balance of aluminum (Al).

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority of Korean Patent Application Number 10-2013-0051292 filed on May 7, 2013, the entire contents of which application are incorporated herein for all purposes by this reference.

TECHNICAL FIELD

The present invention relates to an aluminum alloy used for vehicles parts which may require wear resistance and self lubricity, and a method of preparing the same. In particular, the present invention provides an aluminum alloy having a complex microstructure, which includes wear-resistant particles and self-lubricating soft particles.

BACKGROUND

As an aluminum alloy, a hypereutectic aluminum-iron (Al—Fe) alloy containing from about 13.5 to about 18 wt %, or 12 wt %, of silicon (Si) and from about 2 to about 4 wt % of copper (Cu) has been generally used in a vehicle industry. Since such conventional hypereutectic Al—Fe alloy has a microstructure with primary silicon (Si) particles having a size of from about 30 to about 50 μm, it may have improved wear resistance compared to mere Al—Fe alloys, and thus it is generally used for vehicle parts which may require wear resistance, such as a shift fork, rear cover, swash plate, and the like. An example of commercial alloys may include: an R14 alloy (manufactured by Ryobi Corporation, Japan), a K14 alloy which is similar to the R14 alloy, an A390 alloy which is used for a monoblock or aluminum liner, and the like.

However, such hypereutectic alloys may have problems due to high silicon content, such as, low castability, low impact resistance, and the like. In addition, adjustment of size and distribution of silicon (Si) particles may be difficult and manufacturing hypereutectic alloys may cost more than other general aluminum alloys because of specifically developed process.

Meanwhile, an An-Sn alloy may be another example of self-lubricating aluminum alloy for vehicle parts. The An-Sn alloy may include from about 8 to about 15 wt % of tin (Sn), and further include microstructure of self-lubricating tin (Sn) soft particles, which may reduce friction. Therefore, such An-Sn alloy may be used as a base material of metal bearings used in high frictional contact interfaces. However, this An-Sn alloy may not be suitable for structural vehicle parts due to low strength, for instance, about 150 MPa or less, although the strength may be reinforced by silicon (Si) content.

The description provided above as a related art of the present invention is just merely for helping understanding the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.

SUMMARY OF THE INVENTION

The present invention may provide a technical solution to the above-mentioned problems. Therefore, in one aspect, the present invention provides a novel high-strength and wear-resistant alloy having a microstructure which may be obtained from both hard particles and soft particles thereof. In particular, the novel alloy may have both wear resistance from a hypereutectic Al—Si and self-lubricity from an Al—Sn alloy.

In one exemplary embodiment, the present invention provides a wear-resistant alloy having a complex microstructure, which may include: a range of about 28 to about 38 wt % of zinc (Zn); a range of about 1 to about 3 wt % of tin (Sn); a range of about 6.2 to about 9.4 wt % of silicon (Si); and a balance of aluminum (Al). The wear-resistant alloy may further include a range of about 1 to about 3 wt % of copper (Cu). The wear-resistant alloy may also include a range of about 0.3 to about 0.8 wt % of magnesium (Mg). In addition, the wear-resistant alloy may include a range of about 1 to about 3 wt % of copper (Cu) and a range of about 0.3 to about 0.8 wt % of magnesium (Mg).

In another exemplary embodiment, the present invention provides a wear-resistant alloy having a complex microstructure, which may include: a range of about 28 to about 38 wt % of zinc (Zn); a range of about 1 to about 3 wt % of bismuth (Bi); a range of about 6.2 to about 9.4 wt % of silicon (Si); and a balance of aluminum (Al).

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is an exemplary graph showing a correlation between friction efficient and tin (Sn) content in wt % or zinc (Zn) content in wt % of wear-resistant alloys having a complex microstructure according to an exemplary embodiment of Examples and Comparative Examples with respect to soft particles.

DETAILED DESCRIPTION

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about”.

Hereinafter, various exemplary embodiments of the present invention will be described in detail. The present invention relates to a novel alloy having a complex microstructure, which may include both hard particles and soft particles.

In certain examples of conventional aluminum alloys, alloy elements for forming self-lubricating particles may include tin (Sn), lead (Pb), bismuth (Bi), zinc (Zn) and the like. These alloy elements may not formed be into intermetallic compounds because they may not react with aluminum, and the phase thereof may be separated. Further, these alloy elements may have relatively low melting points, and have self-lubricity for forming a lubricating film while partially melting under a severe friction condition.

Among the above-mentioned four alloy elements, lead (Pb) may be the most suitable element for forming self-lubricating particles when considering both self-lubricity and cost. However, lead is prohibited in vehicles because it is classified as a harmful metal element. In this regard, tin (Sn) may be the most widely used instead of Pb, and bismuth (Bi) may be used occasionally instead of Sn. In contrast, zinc (Zn) may be disadvantageous due to a substantially high melting point compared to Sn and Bi, and substantially low self-lubricity. However, Zn may be added in relatively substantial amount, due to the low cost. Therefore, in consideration of cost competitiveness, Zn may be used for forming soft particles, and partially replacing expensive Sn or Bi.

Additionally, Si or Fe may be an alloy element for forming hard particles. Si or Fe may cause an eutectic reaction together with Al, and form angular hard particles when added in a predetermined amount or more. In an example of aluminum alloys, Si may form hard particles, and may form primary silicon particles. Further, Si may provide wear resistance when added to a binary Al—Si alloy in an amount of about 12.6 wt % or greater. However, when Si is added together with Zn, which is an element for forming soft particles, Si content may be changed according to Zn content to form hard particles. For example, Si content may be about 7 wt % at minimum to about 14 wt % at maximum, when the Zn content is about 10 wt %. When the Si content is less than 7 wt % at minimum, hard particles may not be formed; and when the Si content is greater than about 14 wt % at maximum, the size of hard particles may significantly increase, thereby creating a negative influence on mechanical properties and wear resistance.

In Al—Fe alloys, Fe may be an impurity. However, when an Al—Fe binary alloy contains no Si, and Fe is added in an amount of about 0.5 wt % or less, wear-resistant Al—Fe intermetallic compound particles may be formed, thereby providing wear resistance to the Al—Fe alloy. In contrast, when Fe is added in an amount of about 3 wt % or greater, the intermetallic compound particles may be excessively formed, thereby deteriorating mechanical properties and increasing the melting point. Furthermore, alloy elements for reinforcing the strength of an exemplary aluminum alloy may include Cu and Mg. Cu may be effective in forming intermetallic compounds and increasing strength through a chemical reaction of Cu with Al. The effect of Cu may vary depending on the Cu content, casting/cooling conditions or heat-treatment conditions. Mg may be effective in forming intermetallic compounds and increasing strength through a chemical reaction of Mg with Si or Zn. The effect of Mg also may vary depending on the Mg content, casting/cooling conditions or heat-treatment conditions.

Hereinafter, the present invention will be described in detailed exemplary embodiments.

In one exemplary embodiment, the aluminum alloy may include aluminum (Al) as a main component, and further include a range of about 28 to about 38 wt % of zinc (Zn); a range of about 1 to about 3 wt % of tin (Sn); a range of about 1 to about 3 wt % of copper (Cu); a range of about 0.3 to about 0.8 wt % of magnesium (Mg); and a range of about 6.2 to about 9.4 wt % of silicon (Si) for forming hard particles. When zinc (Zn) is added in an amount of less than about 28 wt %, a sufficient amount of Zn soft particles may not be formed, and thus it may be difficult to obtain sufficient self-lubricity. When zinc (Zn) is added in an amount of greater than about 38 wt %, the solidius line of the aluminum alloy may become substantially low, thereby deteriorating casting conditions.

In addition, tin (Sn) may have greater self-lubricity than zinc (Zn). When tin (Sn) is added in an amount of less than 1 wt %, a sufficient amount of Sn soft particles may not be formed, and thus it may be difficult to compensate for insufficient self-lubricity of Zn soft particles. When tin (Sn) is added in an amount of greater than 3 wt %, additional self-lubricating effects may not be sufficient compared to cost rise, and thus the amount thereof is limited.

Silicon (Si) may form hard particles. When silicon (Si) is added in an amount of less than about 6.2 wt %, primary Si hard particles may not be sufficiently formed, for instance, less than about 0.5 wt %, and thus it may be difficult to ensure wear resistance. When silicon (Si) is added in an amount of greater than about 9.4 wt %, the primary Si hard particles may be excessively formed, for instance, greater than about 5 wt %, and thus these hard particles may be coarsened, thereby creating a negative influence on wear resistance and mechanical properties.

Copper (Cu) may improve mechanical properties, and copper (Cu) may be added in an amount of about 1 wt % or greater to ensure sufficient mechanical properties. However, when copper (Cu) is added in an amount greater than 3 wt %, other elements and intermetallic compounds may be formed to deteriorate the mechanical properties of the aluminum alloy, and thus the amount of copper (Cu) may be limited. Alternatively, magnesium (Mg) may be added instead of Copper (Cu) in an amount of about 0.3 wt % or greater and the mechanical properties of the aluminum alloy may be additionally improved. However, when magnesium (Mg) is added in an amount of about 0.8 wt %, compounds deteriorating the mechanical properties of the aluminum alloy may be formed, and thus the amount of magnesium (Mg) may be limited.

The low frictional characteristics of the Al—Zn—Sn alloy according to an exemplary embodiment of the present invention have been evaluated with respect to soft particles. As shown in FIG. 1, exemplary alloys of Examples and Comparative Examples were prepared while changing the amount of Zn and Sn, and then the changes in friction coefficients of the alloys were measured. As a result, under a condition of about 1 wt % Sn, exemplary 1Sn-28Zn alloys of Examples may obtain desired low frictional characteristics, for instance, friction coefficient of about 0.150 or less, and exemplary 1Sn-26Zn alloys of Comparative Examples may obtain undesired results. Therefore, when Zn is added in an amount of about 28 wt % or greater based on about 1 wt % or greater of Sn, desired low frictional characteristics may be obtained. In addition, when the amount of Sn and Zn increases, satisfactory low frictional characteristics may be obtained. The results of evaluation of wear resistance and mechanical properties of exemplary Al-35Zn-1Sn-xSi alloys of Examples and Comparative Examples are given in Table 1 below.

TABLE 1 Zn Sn Si Cu Mg Si particle Strength Class. Al (wt %) (wt %) (wt %) (wt %) (wt %) fraction (%) (MPa) Comp. residue 35 1 6 2 0.5 0.2 — Example Examples residue 35 1 6.2 2 0.5 0.5 355 residue 35 1 6.4 2 0.5 1 — residue 35 1 9.2 2 0.5 4.8 350 residue 35 1 9.4 2 0.5 5 350 Comp. residue 35 1 9.6 2 0.5 5.2 — Example

In Table, when exemplary Al-35Zn-1Sn-xSi alloys of Comparative Examples, which may include about 0.8 wt % of Si, Si particles in forms of hard particles may be formed in an amount of about 0.2 wt %, and thus it may be difficult to obtain sufficient wear resistance. In contrast, when Si is included in an amount of about 9.6 wt %, Si particles in forms of hard particles may be formed in excessive amounts, for instance, greater than about 5 wt %, and thus Si particles may be coarsened and segregated. Furthermore, when the amount of Si is from about 6.2 to about 9.4 wt %, Si hard particles may be formed in a maximum amount of about 5 wt %, thereby obtaining sufficient wear resistance.

In addition, the strengths of exemplary Al-35Zn-1Sn-xSi alloys may be a range of about 350 to about 355 MPa according to the amount of Si, and thus such alloys may be used as structural materials for vehicle parts. The aluminum alloy according to another exemplary embodiment of the present invention may include: a range of about 28 to about 38 wt % of zinc (Zn); a range of about 1 to about 3 wt % of bismuth (Bi); a range of about 6.2 to about 9.4 wt % of silicon (Si); a balance of aluminum (Al). In particular, bismuth (Bi) may be used as a strong self-lubricating material instead of tin (Sn).

As described above, the wear-resistant alloy having a complex microstructure according to exemplary embodiments of the present invention may have both the wear resistance as of a hypereutectic Al—Si alloy and the self-lubricity as of an Al—Sn alloy, thereby achieving high strength and improved wear resistance.

Although the exemplary embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

What is claimed is:
 1. A wear-resistant alloy having a complex microstructure, comprising: a range of about 28 to about 38 wt % of zinc (Zn); a range of about 1 to about 3 wt % of tin (Sn); a range of about 6.2 to about 9.4 wt % of silicon (Si); and a balance of aluminum (Al).
 2. The wear-resistant alloy of claim 1, further comprising a range of about 1 to about 3 wt % of copper (Cu).
 3. The wear-resistant alloy of claim 1, further comprising a range of about 0.3 to about 0.8 wt % of magnesium (Mg).
 4. The wear-resistant alloy of claim 1, further comprising a range of about 1 to about 3 wt % of copper (Cu) and a range of about 0.3 to about 0.8 wt % of magnesium (Mg).
 5. A wear-resistant alloy having a complex microstructure, comprising: a range of about 28 to about 38 wt % of zinc (Zn); a range of about 1 to about 3 wt % of bismuth (Bi); a range of about 6.2 to about 9.4 wt % of silicon (Si); and a balance of aluminum (Al). 